Soybean protein material and process for production thereof

Abstract: A process for the production of a soybean protein material comprising the step of slow freezing of a solution of a heat-treated soybean protein in the presence of an alkaline earth metal, produces a soybean protein material which comprises a structure in which the layers have grown oriented along the non-cell ice crystals. The soybean protein material produced by the process has, in the raw condition, an extremely smooth mouthfeel such that it melts in the mouth but, when heated, has a mouthfeel extremely similar to that of meat.

Description: The present invention relates to a soybean protein material and a process for production thereof. More particularly, it relates to a soybean protein material having a structure in which the layers are integrally formed oriented or a structure in which the layers are fibrously tearable and a process for production thereof. Various protein materials having texture have been hitherto known. For example, a protein material obtained by winding and binding "yuba" (dried bean curds) has a structure in which the layers are formed concentrically parallel to the surface. Each layer is composed of a film itself and, therefore, such the protein material has the same mouthfeel as that of "yuba" itself in the raw condition and hardly has the meat-like mouthfeel when heated. In addition, a protein material manufactured by using an extruder has no smoothness and softness like "tofu" (bean curd). Such protein material as such has a lamellar (network) and porous structure and hardly has a layered structure. Next, there is known a method for producing a protein material having texture by coagulating and freezing a protein. "Kori-tofu" (freeze-dried bean curd) is obtained, typically, by freezing and aging "tofu" which has been prepared harder. However, "kori-tofu" has a sponge-like and porous (cell-like) structure and no layered structure based on freeze-denaturation. In addition, the formation of the fibrous structure of muscle and the layered structure of muscle bundle by freezing animal fibrous muscle as a raw material is described in JP-B 5-68221. The resulting protein material has a texture based on a fibrous texture. US-A-3,922,359 describes a method of producing solid protein material with a spongy (not layered) texture, which comprises adding an edible divalent salt to a solution of soybean protein in such an amount that the solution becomes turbid white with protein, a part of the protein being still dissolved, freezing the said solution, keeping the solution frozen for from about one to two days, and then thawing and recovering the resultant solid protein material. In three of the Examples the soybean protein solution is heated prior to the addition of the divalent salt. FR-A-2,130,282 describes a process comprising freezing an insoluble protein slurry to produce a product in particular resembling meat. The main object of the present invention is to provide a soybean protein material having good mouthfeel. Another object of the present invention is to provide a process for production of a soybean protein material having good mouthfeel. These objects as well as other objects and advantages of the present invention will become apparent to those skilled in the art from the following description with reference to the accompanying drawings. The inventors searched for a process for production of soybean protein material having good mouthfeel. They found that a soybean protein material having good mouthfeel can be obtained by slow freezing of a soybean protein solution containing a particular metal after heat-treatment and that the resulting protein material has a layered structure. The present invention is based on the above findings and provides a process for production of a soybean protein material which comprises the step of slow freezing of a solution of a heat-treated soybean protein in which precipitates formed from a soybean protein are not present and containing 0.1 to 35% by weight of soybean protein based on the weight of the solution and 0.01 to 5.0% by weight of an alkaline earth metal based on the weight of the crude protein and having a pH of 5 to 9 to obtain soybean protein having a structure in which the layers have grown oriented along the non-cell ice crystals. There is also provided a soybean protein material which comprises a structure in which the layers have grown oriented along the non-cell ice crystals obtainable by slow freezing of a solution of a heat-treated soybean protein in which precipitates formed from a soybean protein are not present and containing 0.1 to 35% by weight of soybean protein based on the weight of the solution and 0.01 to 5.0% by weight of an alkaline earth metal based on the weight of the crude protein and having a pH of 5 to 9. The soybean protein material produced by the process of the present invention has, in the raw condition, an extremely smooth mouthfeel such that it melts in the mouth but, when heated, has a mouthfeel extremely similar to that of meat. In the accompanying drawings: Fig. 1 is a photograph showing a cross section of a lyophilized soybean protein material obtained in Example 1. Fig. 2 is a photograph of a blocky and massy soybean protein material obtained in Example 14. Fig. 3 is a photograph showing the protein material of Fig. 2 which has been torn into the fibers by loosening. First, a process for production of a soybean protein material by slow freezing is explained. Examples of the soybean protein to be used in the present invention are soybean proteins obtained by extracting such products as soybean and defatted soybean, for example, soybean milk, acid-precipitated protein, concentrated soybean protein and isolated soybean protein. As used herein, a solution of a soybean protein or a soybean protein solution refers to a soybean protein solution, soybean dispersion or, when highly concentrated, soybean protein paste, in which precipitates formed from a soybean protein are not present. The solution of soybean protein in the present invention essentially contains an alkaline earth metal in an amount of 0.01 to 5.0% by weight, preferably 0.2 to 1.0% by weight based on the weight of the crude protein. The strength of the properties of the protein material of the present invention can be regulated by the amount of an alkaline earth metal. As the amount of the alkaline earth metal grows larger, the strength is increased. As the amount of the alkaline earth metal decreases, the resulting protein material is liable to have a smooth mouthfeel between that of a solid and that of a liquid. When the amount of the alkaline earth metal is below 0.01% by weight, the layered structure is not formed. On the other hand, when the amount is above 5.0% by weight, the structure of the protein material becomes different from the layered structure. The alkaline earth metal may be used as its salt or hydroxide which dissociates into ions in the aqueous system. Examples of the alkaline earth metal are calcium and magnesium. These alkaline earth metals can be used alone or in combination. Calcium is preferably used from a practical or taste point of view. Any calcium compound may be used as calcium, for example, calcium chloride, calcium hydroxide or calcium sulfate. One or more of these calcium compounds may be used. The calcium compounds may be used together with an alkaline earth metal other than calcium. The concentration of the soybean protein solution containing an alkaline earth metal is 0.1 to 35% by weight. When the concentration is below 0.1% by weight, the formation of the desired layered structure is difficult even when the soybean protein solution is frozen in the next step. On the other hand, when the concentration is above 35% by weight the formation of the desired layered structure is difficult because the soybean protein solution is held in the flowing state with difficulty even when it is converted into a slurry. A soybean protein solution containing an alkaline earth metal is suitably heated at a temperature of not lower than 60 °C for longer than one second, preferably at a temperature of 80 °C to 160 °C for not shorter than 5 seconds, but not longer than 1 minute at a temperature above 100 °C. This heat-treatment has not only pasteurizing but also freeze-denaturation enhancing effects. As described above, it is important that precipitates formed from a soybean protein solution containing an alkaline earth metal are not present upon freezing. Precipitates are not formed from a soybean protein solution normally at a pH range of 5 to 9, preferably 6 to 8, more preferably 6.5 to 7.5, depending upon the concentration. At pH around 4.5 which is the isoelectric point of a soybean protein, a soybean protein solution is converted into an insoluble slurry. In this state, a soybean protein material having the desired layered structure cannot be obtained, which results in a texture like "kori-tofu". In addition, too high a pH is also not preferable since the desired layered structure is hardly obtained and, moreover, the flavor and color tone are diminished. Protein other than soybean protein, starch, lipid, seasoning, coloring agent and flavor agent may be optionally used together in addition to a soybean protein as the main raw material. By the use of these optional components, a material obtained by cooking, freezing and thawing the above soybean protein solution has a smooth mouthfeel and, as such, can be eaten tastily. By using gluconodeltalactone in the step after a soybean protein solution is heated, a freeze-denatured soybean protein material may be heated to obtain such effects that the resulting texture becomes firmer due to decrease in pH by degradation of gluconodeltalactone. A hydrated protein thus prepared is subjected to slow freezing. Slow freezing can afford a structure in which the layers have grown. Thereupon, as the rate of slow freezing grows lower, the layers form planes and, therefore, become difficult to be torn into fibers. On the other hand, as the rate of slow freezing grows higher, the layers become tearable into fibers and the macroscopic appearance becomes more fibrous. However, when the rate of slow freezing is too high (so-called rapid drying), the degree of freeze-denaturation is decreased and thereby texturization becomes difficult. The rate of slow freezing for changing the structure in which layers have grown into the structure in which the layers are fibrously tearable depends upon the size and shape of the desired soybean protein material. Normally, when the temperature reduction rate at the surface of the soybean protein material is lower than 0.4 °C per minute, the layers form planes and further form a structure which is difficult to be fibrously torn. As the rate grows higher than 0.4 °C per minute, there is a tendency for a structure in which the layers are fibrously tearable to be formed or the layers are converted into macroscopically fibrous material. In slow freezing, the time for passing through the maximum ice crystals forming zone is required to be not shorter than 30 minutes. The layers which are formed at the time of passing through the maximum ice crystals forming zone in the central part of a hydrated protein of not shorter than 2 hours are liable to be hardly torn into fibers. As the time for passing through the maximum ice crystals forming zone grows shorter than 2 hours, there is a tendency that the structure in which the layers are fibrously tearable is formed or the layers are converted into macroscopically fibrous material. In order to decrease the rate of slow freezing, cooling is suitably carried out with air having a low heat conductivity. Freezing is suitably carried out normally in the atmosphere at -20 °C to -30 °C. In order to increase the rate of slow freezing, cooling is suitably carried out by contact with a liquid brine which has a high heat conductivity (normally at -20 ° to -25 °C). Normally, freezing can be carried out at a temperature of not lower than -2 °C. Practically, -2 °C to -60 ° is suitable. In particular, slow freezing can be effectively carried out in the atmosphere at -20 °C to -30 °C. The process where the layered or fibrous structure is formed can be considered as follows: In the case where the rate of slow freezing is lower, when a hydrated protein is placed in the atmosphere at a temperature of not higher than the freezing point, ice crystals are formed in a linear fashion on the surface and they grow in the heat conducting direction (towards the central part) in the course of time. At the same time, a protein begins to be freeze-denatured and the protein and ice crystals form a layered structure starting from the surface then in the heat conducting direction (towards the central part), that is, from a lower temperature part to a higher temperature part. As the rate of slow freezing grows higher, ice crystals become finer and it is presumed that, as a result, the structure in which the formed protein layers are fibrously tearable is formed or, since the formed ice crystals become shorter from linear to dot-like, the macroscopically fibrous structure is formed. Therefore, for example, when three sides of a hydrated protein are thermally insulated and the remaining side is exposed to cold air or liquid brine, linear or dot-like ice crystals are first formed at the open part of the surface and, then, ice crystals grow in a plane-like or linear fashion along the coldness delivery direction. This is accompanied by freeze-denaturation of a soybean protein to give a layered material in which an ice crystals layer and a freeze-denatured protein layer are arranged layered one after the other or a macroscopically fibrous material. In the other case, for example, when all the peripheral parts of a hydrated protein are exposed to the cold air or liquid brine, the protein layers or fibers are formed inward via ice crystals. That is, as freezing proceeds from the peripheral parts to the central part, linear or dot-like ice crystals are first formed and the formed crystals grow into inward plane-like or linear ones. When a plurality of such crystals grow competitively in the inner part, the crystals having the lower growth rate stop growing and the crystals having the higher growth rate continue to grow further until the next competition (Fig. 1). This is why the degree of plane-like or linear growing (the depth of the growing tip) becomes different. Alternatively, for example, when only two opposite sides are exposed to the cold air or liquid brine, the linear or dot-like crystals are first formed on both surfaces and both crystals formed grow inwardly parallel to each other into the plane-like linear plane ones. Both of the adjacent growing crystals rarely compete and continue to grow in only one direction. Finally, they form a collision plane and stop growing (Fig. 3). Alternatively, for example, when a part of the periphery is brought into contact with a brine and the contacted part is randomly changed in the course of time, the direction of the growing crystals can be randomly changed three-dimensionally. A protein is freeze-denatured while compartmented by the plane-like or linear ice crystals, to give a layered structure or a macroscopically fibrous structure. Although such plane-like or linear ice crystals are not formed when conventional soybean protein solution is frozen, the above ice crystals are formed when a soybean protein solution in the present invention is frozen under the above-mentioned conditions. For freezing, any containers made of a material having resistance to freezing can be used, for example, a container made of a metal such as stainless steel or aluminium, or, for example, soft plastic. The soybean protein material thus prepared can be thawed or thawed and dehydrated after slow freezing. The thawed soybean protein material can be eaten as such or used as a food material. Alternatively, the protein material may be dehydrated from the point of view of, for example, form of utilization, distribution, and storage. Dehydration can be carried out by known methods such as centrifugation or pressing. Normally, pressure dehydration is preferable since a firm texture can be obtained. Upon pressure dehydration, the stress can be applied by press to decrease the content of water contained between the protein layers or in the layers themselves. Pressure application has the effect of binding the protein more tightly to afford a firmer texture. The thawed or thawed and dehydrated soybean protein material can be further heated. While the thawed soybean protein material or the dehydrated soybean protein material has a soft mouthfeel such that it melts in the mouth before heating, it has a meat-like mouthfeel after heating. When the thawed soybean protein material is heated as such, it is separated into each unit layer or into each layer comprising a plurality of unit layers or macroscopic fibers are separated, in a solution, to give a flake-like or fibrous material. Alternatively, as described for the above dehydration, when the protein material is heated while stress is applied to the material to hold the layers or fibers tight, the layers or fibers adhere together to give a block-like and meat-like protein material having a compact structure. This block-like and meat-like protein material can by manually peeled or torn into fibers. The stress can be applied in any fashion. For example, a method described for the above hydration, a method by filling a protein material in a casing tube or the like and heating at a sufficient temperature to heat set a protein or the like can be used. Heating is carried out sufficiently to a thermal historical extent that the layers or fibers of a soybean protein material adhere together and are set (normally at a temperature of not lower than 80 °C). The above-described frozen soybean protein material, thawed soybean protein material, dehydrated soybean protein material or heated soybean protein material can be further dried. Drying can be carried out by a known method such as microwave drying, fry drying and hot air drying. As described above, the soybean protein material of the present invention has a structure in which the layers have one- to three-dimensionally grown and are oriented along the tracks of a plurality of non-cell ice crystals, depending upon the extent of the rate of slow freezing. The oriented structure can be a structure in which the layers have grown or a structure which can be easily loosened into fibers. In some cases, the tracks of the growing tips of ice crystals form a nodular plane. First, a soybean protein material having a structure in which the layers have grown one to three-dimensionally and are oriented along the tracks of a plurality of the non-cell ice crystals will be explained. The soybean protein material has a structure in which the layers have grown via the tracks of a plurality of non-cell ice crystals, for example, the tracks of ice crystals which have grown in a plane-like fashion. As used herein, the ice crystals which have grown in a plane-like fashion refers to the planes of the ice crystals which were formed first in a linear fashion on the surface of a hydrated soybean protein material by freezing and have grown in a plane-like fashion in the coldness conducting direction. As used herein, the tracks of the ice crystals which have grown in a plane-like fashion includes not only the condition where ice crystals grown in a plane-like fashion are present but also the condition where ice crystals have disappeared for example by melting or drying. As used herein, the layers refers to the plane-like layers which were formed by freeze-denaturation of a soybean protein via the above-described tracks of the plane-like ice crystals (in other words, while compartmented by the above-described plane-like ice crystals). The direction of the layers therein is seldom constant because of the influence of the freezing conditions and a plurality of unit layers are formed normally at from a slight to large angle and in different directions from each other. As used herein, the layered structure refers to the structure formed by the combination of a plurality of the above-described layers. This layered structure is the structure in which unit layers are overlapped arbitrarily and arranged in different directions at a slight angle from each other. This is because the linear ice lines which are formed first on the cold air side of a soybean protein material are not unidirectional and these linear ice lines grow in the coldness conducting direction to form plane-like ice crystals. Therefore, a unit layer itself is not necessarily a uniform plane but a plurality of layers are overlapped arbitrarily. Next, when the rate of slow freezing is increased, the structure in which the layers are torn into the fibers (can be loosened) is formed, or the structure in which the layers are converted into macroscopically fibrous materials and are further torn into the fibers is formed. A soybean protein material having a structure which is fibrously tearable refers to a structure which is macroscopically layered or fibrous but the layers or fibers therein can be torn into finer fibers. Ice crystals grow in the coldness conducting direction. However, since the growth rate of ice crystals in a soybean protein solution in the present invention has dispersion, the tip tracks become not linear but burred in a nodular plane fashion. The extent of burrness of the nodular plane becomes higher or lower depending for example upon the freezing conditions and the form of the container. The soybean protein material of the present invention which has been heat set is stable at a pH range equal to or below the neutral point. On the other hand, soybean protein which has not been heat set is stable at a non-limited pH range, suitably, at pH not higher than 9. As the pH becomes lower, the hardness of the protein material is increased, which results in a firm mouthfeel. In the case of a soybean protein material of the present invention which has been thawed among the protein materials which have not been heat set, the pH can be arbitrarily selected when the protein material is eaten in a shorter period of time after thawing or is utilized for later heat-cooking. However, in other cases, the suitable pH range is normally around neutral to acidic. This is because a non-heat set soybean protein material has properties such that it dissolves in an aqueous alkaline medium when allowed to stand therein for a long period of time. A soybean protein material of the present invention has different physical properties depending upon whether it has been heat set or not. This difference is explained below. First, a soybean protein material which has not been heat set will be explained. As used herein, the term "heat set" refers to the state where a soybean protein material is heat-denatured by heating to a extent that it does not dissolve in an aqueous medium at any pH range. Examples of soybean protein material which has not been heat set are a protein material having the structure in which ice is intervened between layers or fibers, or water is intervened therebetween, or gas is intervened therebetween, or nothing is intervened therebetween and the respective layers or fibers are brought into direct contact with each other. A soybean protein material which has not been heat set is apparently gel-like as such or when water is intervened therebetween, but it has a smooth mouthfeel such that it melts in the mouth in spite of the layered or fibrous structure. Next, a soybean protein material which has been heat set will be explained. A soybean protein material which has been heat set has a structure in which the layers or fibers are separated in a layered or fibrous fashion, showing a shape similar to a flake-like or fibrous one. In addition, a protein material obtained by applying stress thereto with a press or the like to exclude water present between the layers or fibers and thereby to hold the layers or fibers tight and thereafter heating it has a block-like structure and excellent meat-like mouthfeel. Next, a material which has been heat set or not may be in a dried state. Examples of drying methods are lyophilizing, heat frying and fry drying. The drying method can be arbitrarily selected depending upon use, such as daily dish and convenience food, dispersion or storage. The following Examples and Comparative Examples further illustrate the present invention but are not to be construed to limit the scope thereof. Example 1 1 part by weight of defatted soybean was extracted with 12 parts by weight of water to give soybean milk. Hydrochloric acid was added to the soybean milk to adjust pH to 4.5, to give an acid-precipitating soybean protein. Then, water was added to the acid-precipitating protein to a protein concentration of 12% by weight. 1.56% of calcium hydroxide was added thereto and sodium hydroxide was added thereto to neutralize to pH 6.8. Then, heating was carried out at 140 °C for 15 seconds. While the protein solution remained hot before cooling (at least 40 °C), 0.79% of calcium chloride was added thereto and the solution was stirred well to react with the calcium. The resulting protein solution was placed in a 400 milliliter stainless steel container. The container was placed in a small size environmental testing apparatus (manufactured by TABAI ESPECK K.K.). The protein solution was cooled to -20 °C at a cooling rate (the surface temperature reducing rate) of -0.2 °C/minute to freeze. The ice crystal formation initiating temperature was -0.5 °C and the time for passing through the maximum ice crystals forming zone was 2 hours and 10 minutes. This frozen protein material was thawed and found to have an extremely smooth mouthfeel like liquid. The protein material was observed to have a layered and gel-like texture. However, different from a gel containing water therein uniformly, the protein material had a structure in which a soybean protein was freeze-denatured and the soybean protein layers had grown through water. Separately, this freeze-texturized material was thawed and the pH was adjusted to 5.5 to 6.0 with lactic acid. As the pH was adjusted to a lower region, the mouthfeel became harder. Then, the material was centrifuged to dehydrate to a water content of 70%. At this point, the protein material had a layered structure in which the plane-like layers had grown in the ununiform direction. The protein material was eaten and found to have a texture which was relatively soft and could be masticated. After this, when dehydration was carried out more strongly, the protein material had a harder mouthfeel. Then, the resulting dehydrated material was heat-treated at 80 °C for 30 minutes and cooled. The resulting material was eaten and found to have a mouthfeel extremely similar to that of meat, different from a smooth mouthfeel as in the gel. The protein material was observed as follows: the layered texture remained unchanged but the soybean protein underwent both freeze-denaturation and heat-denaturation, which resulted in a harder and firmer texture. This is the reason why the material had the meat-like mouthfeel. A photograph of the lyophilized soybean protein material (obtained by vacuum-drying a frozen material without thawing) obtained in Example 1 is shown in Fig. 1. Example 2 One part by weight of defatted soybean was extracted with 12 parts by weight of water to give soybean milk. Hydrochloric acid was added to the resulting soybean milk to adjust to pH 4.5, to give an acid-precipitating soybean protein. Crude protein per dried solid of this soybean protein was 92%. Then, water was added to the acid-precipitating soybean protein to a protein concentration of 12% by weight. To this was added 1.56% of calcium hydroxide and sodium hydroxide was added to neutralize to pH 6.8. A soybean oil was added thereto in an amount of 50% based on the protein amount and the mixture was emulsified by a conventional method, to give a solution of soybean protein emulsion. Then, the solution was heated at 140 °C for 15 seconds. While the protein solution remained hot before cooling (at least 40 °C), 0.79% of calcium chloride was added thereto and the protein solution was stirred to react with the calcium. The resulting protein solution was frozen as in Example 1. That is, the protein solution was cooled to -20 °C at the cooling rate (the surface temperature reduction rate) of -0.2 °C/minute to freeze. After this, the ice crystal forming temperature in the central part was -0.5 °C. The time for passing through the maximum ice crystals forming zone during which the temperature passed -0.5 °C and further began to fall was 2 hours and 10 minutes. The frozen material was thawed, eaten and found to have an extremely smooth mouthfeel like liquid. The material was carefully observed to have a layered gel-like texture. Different from a gel containing water uniformly therein, the material had a structure in which a soybean protein was freeze-denatured and the soybean protein layers had grown through water. Separately, the freeze-texturized material was thawed and the pH was adjusted to pH 5.5 to 6.0 with lactic acid. As the pH was adjusted to a lower region, the mouthfeel became harder. Then, the material was centrifuged to dehydrate to a water content of 70%. After this, as dehydration was carried out to a higher extent, the mouthfeel became harder. Then, the dehydrated material was heat-treated at 80 °C for 30 minutes and cooled. The resulting material was eaten and found to have a mouthfeel extremely similar to that of meat, different from the smooth mouthfeel as the gel. The material was observed as follows: the layered texture remained unchanged but a soybean protein underwent both freeze-denaturation and heat-denaturation, which resulted in a harder and firmer texture. This is the reason why the material had a meat-like mouthfeel. Separately, the above-described soybean protein material having a layered structure via water was lyophilized. Water was added to the lyophilized material to reconstitute to give a material which had similar properties to those of the material before lyophilizing. Example 3 A soybean protein material having a layered structure was obtained in the same manner as in Example 1 except that calcium hydroxide and sodium hydroxide were used in place of calcium hydroxide and calcium chloride. 1.96% of calcium hydroxide was added to an acid-precipitating protein having a protein concentration of 12% and thereafter sodium hydroxide was added to neutralize to a pH 6.8, or 0.78% of calcium chloride was added thereto and sodium hydroxide was added to neutralize to a pH 6.8. Then, the material was heated at 140 °C for 15 seconds. After cooling, the material was cooled to -20 °C at a cooling rate (the surface temperature reduction rate) of 0.2 °C/minute to freeze as described in Example 1. The resulting frozen material had a layered texture through water and had an extremely smooth mouthfeel like liquid in spite of being solid. Further, in the same manner as in Example 1, pH adjustment, dehydration and heating were carried out to give a soybean protein texturized material having a meat-like mouthfeel. Example 4 A soybean protein material was obtained in the same manner as in Example 1 except that calcium hydroxide and calcium chloride were used in an amount of 0.2% by weight as calcium per crude protein of soybean protein. The resulting protein material had an extremely soft mouthfeel. The material had a texture in which a layered structure was formed and the layers in the texture were loosened when gently stirred with a glass bar. Comparative Example 1 A comparative soybean protein material was obtained in the same manner as in Example 1 except that calcium hydroxide and calcium chloride were used in an amount of 0.005% by weight as calcium per crude protein of soybean protein. Although ice crystals were formed in a layered fashion by freezing, the material was found to be pasty, when thawed, without formation of soybean protein texture. Example 5 A soybean protein material was obtained in the same manner as in Example 1 except that calcium hydroxide and calcium chloride were used in an amount of 3% by weight as calcium per crude protein of soybean protein. The resulting soybean protein material was soft. However, its mouthfeel was harder in comparison with that of protein material obtained according to the same method as in Example 1 to 3. Comparative Example 2 A comparative soybean protein material was obtained according to the same method as in Example 1 except that calcium hydroxide and calcium chloride were used in an amount of 6% by weight as calcium per crude protein of soybean protein. The soybean protein solution coagulated and lost its flowability before freezing. When the coagulated material was frozen, a sponge-like structure was formed but a layered structure was not obtained, which resulted in "kori-tofu"-like soybean protein material. The resulting protein material had not a smooth but a "kori-tofu"-like mouthfeel. Example 6 A soybean protein solution before freezing was obtained in the same manner as in Example 1. Then, the solution was adjusted to pH 6.5 and frozen in the same manner as in Example, to give a soybean protein material. The soybean protein solution in this Example had a lower viscosity in comparison with that of a soybean protein solution before freezing obtained in the same manner as in Example 1. The solution in this Example was frozen and thawed to give a soybean protein which was eaten and found to have a harder and stiffer mouthfeel in comparison with that of a soybean protein material obtained in the same manner as in Example 1. The protein material in this Example had a layered structure through water. Further, the protein material of this Example was heated in the same manner as in Example 1. The resulting material had a harder and meat-like mouthfeel in comparison with that of a material obtained in the same manner as that in Example 1. Comparative Example 3 A comparison soybean protein material was obtained in the same manner as in Example 5 except that the pH was adjusted to 4.5. The soybean protein solution before freezing coagulated to give a "tofu"-like material which was frozen to obtain a sponge-like and "kori-tofu"-like texturized material. The resulting material had a harder mouthfeel than that of the material in Example 5, resulting in a "kori-tofu"-like mouthfeel. Example 7 A soybean protein material was obtained in the same manner as in Example 5 except that the pH of the soybean protein solution upon freezing was adjusted to 8.0. The resulting soybean protein material was extremely soft in comparison with the soybean protein material obtained in the same manner as in Example 1. The protein material had a layered structure through water but its texture was easily loosened in a layered fashion when gently stirred with a glass bar. Separately, the resulting protein material was heated in the same manner as in Example 1. The heated material had a meat-like mouthfeel. Comparative Example 4 A comparative soybean protein material was prepared in the same manner as in Example 6 except that the pH was adjusted to 11. A layered texture was formed by freezing. However, when thawed, the protein material lost the soybean protein texture and became pasty. Example 8 A soybean protein material was obtained in the same manner as in Example 1 and freezing performed except that the pH of the soybean protein solution upon freezing was adjusted to 6.8. A layered structure which was formed by freezing was not loosened even when allowed to stand at 20 °C or heated at 80 °C. Example 9 A soybean protein material having a layered structure with needle ice crystals was obtained in the same manner as in Example 1 and freezing performed except that the soybean protein solution upon freezing was adjusted to pH 7.5. After thawing, the protein material was melted by allowing to stand at 20 °C or heating at 80 °C. The pH was readjusted to 6.8 after thawing. After pH re-adjustment, the soybean protein material was heated but it did not melt. Example 10 A soybean protein solution before freezing obtained in the same manner as in Example 1 was pre-treated by heating at 80 °C and thawed in the same manner as in Example 1, to obtain a soybean protein material which was thawed. The resulting protein material was extremely soft. Its texture was easily loosened by gently stirring with a glass bar. However, the soybean protein material had a layered structure through water. Comparative Example 5 A comparative soybean protein material was obtained in the same manner as in Example 10 except that the soybean protein solution before freezing obtained in the same manner as in Example 1 was pre-treated by heating at 55 °C for 15 seconds. When the resulting soybean protein material was gently stirred with a glass bar, it turned white due to insufficient partial texturization. Example 11 1250 milliliters of a soybean protein solution before freezing prepared in the same manner as in Example 1 was frozen at an ambient temperature of -10°C in the same manner as in Example 1. After this, the cooling rate (the surface temperature reduction rate) was 0.02 °C per minute. At this point, the ice crystals forming temperature in the central part was -0.5 °C and the time for passing through the maximum ice crystals forming zone during which the temperature passed this temperature region and began to fall further was 4 hours and 50 minutes. The resulting soybean protein material had a texture in which a layered structure was formed through water and was extremely soft. In addition, when the solution is frozen, the change in temperature is different between the surface and the central part, depending upon the volume and form thereof. Therefore, the change in temperature in the surface part was adopted as the change in cooling temperature. Furthermore, since the change in temperature at the surface part upon freezing was not linear, the cooling rate was obtained by linear approximation by connecting a point where cooling was initiated and that where the temperature reached an ambient temperature. Example 12 A solution of soybean protein emulsion obtained in the same manner as in Example 2 was heated at 140 °C for 15 seconds and 0.79% of calcium chloride was added thereto to react with the calcium while stirring, to obtain a protein solution (referred to as "Ca protein solution" hereinafter). Gluconodeltalactone (referred to as "GDL" hereinafter) was added thereto in an amount designated in Table 1 per crude protein of Ca protein solution and the mixture was cooled to -20 °C at the cooling rate (the surface temperature reduction rate) of -0.2 °C and frozen. After this, the time for passing through the maximum ice crystals forming zone was 2 hours and 10 minutes. This frozen material was thawed, dehydrated with pressing (to a water content of 70%) and treated by heating at 80 °C for 30 minutes. The pH and mouthfeel of the soybean protein food material after heating are also shown in Table 1. GDL pH Mouthfeel 1% 6.6 Soft and meat-like 2% 6.2 Soft and meat-like 2.5% 5.9 Slight resistance to the teeth 3% 5.7 Slightly hard and meat-like 5% 5.1 Hard and meat-like 8% 4.5 Hard and meat-like As can be understood from Table 1, when GDL has been added, the pH adjusting step can be omitted thereafter and the mouthfeel can be pre-regulated. Example 13 Defatted soybean was extracted with water (15 times w/w) to obtain soybean milk. Hydrochloric acid was added to the soybean milk to adjust to a pH 4.5, to obtain an acid-precipitating soybean protein. The crude protein was 92% per dried solid. Then, the concentration of the acid-precipitating soybean protein was adjusted to 12%. 1.56% of calcium hydroxide and 0.39% of calcium chloride were added to the acid-precipitating soybean protein, 0.8% of sodium chloride was further added and sodium hydroxide was added to adjust to pH 6.5. A soybean oil was added in an amount of 50% based on the weight of crude protein and the mixture was emulsified using a homomixer (manufactured by Tokushukikakogyo K.K.) under the condition of 4000 rotations/sec to obtain a solution of soybean protein emulsion. Then, the solution was heated at 140 °C for 15 seconds and cooled to 5 °C. To this solution was added 0.3% of gluconodeltalactone to obtain a soybean protein emulsion preparation. 1800 cc of this soybean protein emulsion preparation was placed in a stainless steel container (70 mm in length, 112 mm in width and 105 mm in height) in which the bottom and two sides thereof were thermally insulated with expanded polystyrene and was frozen at -30 °C in an air-cooling type refrigerator. The temperature in the central part was measured in the freezing step to obtain a time for passing through the maximum ice crystals forming zone of 6 hours. A soybean protein texturized material obtained by freezing had a layered texture through the tracks of ice crystals which had grown in a plane-like fashion. When one carefully tried to peel, the layers were peeled in a layered fashion although a part of layers were bound slightly to each other. The protein material was eaten and found to have excellent masticating properties. Example 14 One part by weight of defatted soybean was extracted with 12 parts by weight of water to obtain soybean milk. Hydrochloric acid was added to the soybean milk to adjust to pH 4.5, to obtain an acid-precipitating soybean protein. Crude protein per dried solid of the soybean protein was 92%. Then, the concentration of the acid-precipitating soybean protein was adjusted to 12%, 1.56% of calcium hydroxide and 0.39% of calcium chloride were added thereto, 0.8% of sodium chloride was further added thereto and sodium hydroxide was added to neutralize to pH 6.5. A soybean oil was added thereto in an amount of 50% based on the weight of protein and the mixture was emulsified at 4000 rotation/sec using a homomixer (manufactured by Tokushukikakogyo K.K.) to obtain a solution of soybean protein emulsion. Then, the solution was heated at 140 °C for 15 seconds and cooled to 5 °C. To this solution was added 0.3% of gluconodeltalactone to obtain a soybean protein preparation. 1800 cc of this preparation was placed in a stainless steel container (70 mm in length, 112 mm in width and 105 mm in height) in which the bottom and two sides were thermally insulated with the expanded polystyrene and was frozen at -23 °C in a cooling brine containing calcium chloride. The temperature in the central part was measured in the freezing step to obtain the time for passing through the maximum ice crystals forming zone of 55 minutes. Further, this frozen material was thawed and warmed with warm water so that the temperature in the central part became 40 °C. Then, this texturized material was taken out of the container and dehydrated with pressing (to a water content of 70%) in a direction parallel to the fibers. The resulting texturized material was packaged sealingly under vacuum, heated with warm water so that the temperature in the central part became 80 °C and cooled thereafter. The cross section of the resulting soybean protein texturized material was observed to be layered as shown in Fig. 2 (The cross section is seen in the upper part of the photograph). The protein material was a blocky mass in which the fine fibers were oriented in one direction and bound together. The blocky mass had a meat-like texture which was loosened into fibers in only one direction when torn as shown in Fig. 3. The soybean protein texturized material had good mouthfeel.

Claims: A process for production of a soybean protein material which comprises the step of slow freezing of a solution of a heat-treated soybean protein in which precipitates formed from a soybean protein are not present and containing 0.1 to 35% by weight of soybean protein based on the weight of the solution and 0.01 to 5.0% by weight of an alkaline earth metal based on the weight of the crude protein and having a pH of 5 to 9 to obtain soybean protein having a structure in which the layers have grown oriented along the non-cell ice crystals, wherein the alkaline earth metal is added before the solution is heated. A process according to claim 1 further comprising the steps of thawing the frozen soybean protein material or further dehydrating the thawed soybean protein material. A process according to claim 2 further comprising the step of heating the thawed soybean protein material or the dehydrated soybean protein material. A process according to claim 2 or 3 further comprising the step of drying the heated soybean protein material. A soybean protein material which comprises a structure in which the layers have grown oriented along the non-cell ice crystals obtainable by slow freezing of a solution of a heat-treated soybean protein in which precipitates formed from a soybean protein are not present and containing 0.1 to 35% by weight of soybean protein based on the weight of the solution and 0.01 to 5.0% by weight of an alkaline earth metal based on the weight of the crude protein and having a pH of 5 to 9, wherein the alkaline earth metal is added before the solution is heated. A soybean protein material according to claim 5 wherein the oriented structure has a structure in which the layers have grown. A soybean protein material according to claim 5 or 6 wherein the oriented structure is easily torn into fibers. A soybean protein material according to claim 5, 6 or 7 wherein the tracks of the growing tips of ice crystals have formed a nodular plane.

Inventors: HIROTSUKA MOTOHIKO, MORIKAWA SEIJI, SAITO TOSHIAKI, HIROTSUKA, MOTOHIKO, MORIKAWA, SEIJI, SAITO, TOSHIAKI
Applicants: FUJI OIL CO LTD, FUJI OIL COMPANY, LIMITED
Application year: 1994
Main classification: A23J3
IPC codes: A23J3